Thermal Noise Research Articles

Optical properties of germania and titania at 1064 nm and at 1550 nm

One of the main noise sources in current gravitational-wave detectors is the thermal noise of the high-reflectivity coatings on the main interferometer optics. Coating thermal noise is dominated by the mechanical loss of the high-refractive index material within the coating stacks, Ta2O5 mixed with TiO2 . For upgrades to room-temperature detectors, a mixture of GeO2 and TiO2 is an interesting alternative candidate coating material. While the rather low refractive index of GeO2 increases with increasing TiO2 content, a higher TiO2 content results in a lower threshold temperature before heat treatment leads to crystallisation, and potentially to a degradation of optical properties. For future cryogenic detectors, on the other hand, a higher TiO2 content is beneficial as the TiO2 suppresses the low-temperature mechanical loss peak of GeO2. In this paper, we present the optical properties of coatings—produced by plasma-assisted ion-beam evaporation—with high TiO2 content at 1550 nm, a laser wavelength considered for cryogenic gravitational-wave detectors, as a function of heat-treatment temperature. For comparison, the absorption of pure GeO2 was also measured. Furthermore, results at the currently-used wavelength of 1064 nm are presented.

Reducing construction noise: sound masking effect on soundscape dominated by construction noise

AbstractPeople move to cities to enjoy the conveniences of modern life, but the resulting population growth comes with issues such as increased noise. While public awareness of noise pollution is increasing, noise emanating from construction sites remains a source of complaint. Despite the actions taken by different parties to control construction noise, newly constructed structures continue to exacerbate the harmful consequences of noise. The acoustic environment in some areas of cities, such as London, can no longer provide the tranquility expected by residents, and the risk of daily disruptions for those living near construction sites is high. Given the various limitations and complications of current construction noise control methods, the campaign to limit construction noise must embrace other strategies. Sound masking can potentially abate noise without resorting to time-consuming procedures. In this paper, five raw construction noise datasets were collected around an existing noise-sensitive premise. Five masker sound datasets were recorded to form seven mixed sounds to create a comparative experiment on masking construction noise. A case study and additional research are presented to demonstrate the mechanism of sound masking and to investigate the factors involved in effectively masking construction noise using the sound masking concept. Based on the case study and theoretical research findings, suggestions for masker selection of specific noise datasets and conclusions regarding ideal sound simultaneous masking of construction noise are provided.

Multi-tracing the primordial Universe with future surveys

The fluctuations generated by Inflation are nearly Gaussian in the simplest models, but may be non-Gaussian in more complex models, potentially leading to signatures in the late Universe. In particular, local-type primordial non-Gaussianity induces scale-dependent bias in tracers of the matter distribution. This non-Gaussian imprint in the tracer power spectrum survives at late times on ultra-large scales where nonlinearity is negligible. In order to combat the problem of growing cosmic variance on these scales, we use a multi-tracer analysis that combines different tracers to maximise any primordial signal. Previous work has investigated the combination of a spectroscopic galaxy survey with a 21 cm intensity mapping survey in single-dish mode. We extend this work by considering instead the case where the 21 cm intensity mapping survey is optimised for interferometer mode. As examples, we use two multi-tracer pairs of surveys: one at high redshift (1≤z≤2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1\\le z\\le 2$$\\end{document}) and one at very high redshift (2≤z≤5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2\\le z\\le 5$$\\end{document}). The 21 cm surveys are idealised surveys based on HIRAX and PUMA. We implement foreground-avoidance filters and use detailed models of the interferometer thermal noise. The galaxy surveys are idealised surveys based on Euclid and MegaMapper. Via a simple Fisher forecast, we illustrate the potential of the multi-tracer. Our results show a ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim $$\\end{document} 20–30% improvement in precision on local primordial non-Gaussianity from the multi-tracer. Furthermore, we investigate the effects on constraints of varying the parameter of non-Gaussian galaxy assembly bias and of varying the parameters of the intensity mapping foreground filters. We find that the non-Gaussian galaxy assembly bias parameter causes a greater change in the constraints on local primordial non-Gaussianity than the foreground filter parameters.

Atto-Scale Noise Near-Infrared Organic Photodetectors Enabled by Controlling Interfacial Energetic Offset through Enhanced Anchoring Ability.

The near-infrared (NIR) sensor technology is crucial for various applications such as autonomous driving and biometric tracking. Silicon photodetectors (SiPDs) are widely used in NIR applications; however, their scalability is limited by their crystalline properties. Organic photodetectors (OPDs) have attracted attention for NIR applications owing to their scalability, low-temperature processing, and notably low dark current density (JD), which is similar to that of SiPDs. However, the still high JD (at NIR band) and few measurements of noise equivalent powers (NEPs) pose challenges for accurate performance comparisons. This study addresses these issues by quantitatively characterizing the performance matrix and JD generation mechanism using electron-blocking layers (EBLs) in OPDs. The energy offset at an EBL/photosensitive layer interface determines the thermal activation energy and directly affects JD. A newly synthesized EBL (3PAFBr) substantially enhances the interfacial energy barrier by forming a homogeneous contact owing to the improved anchoring ability of 3PAFBr. As a result, the OPD with 3PAFBr yields a noise current of 852 aA (JD = 12.3 fAcm⁻2 at V → -0.1V) and several femtowatt-scale NEPs. As far as it is known, this is an ultralow ofJD in NIR OPDs. This emphasizes the necessity for quantitative performance characterization.

Current and shot noise in a normal metal–superconductor junction driven by spin-dependent periodic pulse sequence

Current and shot noise in a normal metal–superconductor junction driven by spin-dependent periodic pulse sequence

Infrared photodetection in graphene-based heterostructures: bolometric and thermoelectric effects at the tunneling barrier

Graphene/hBN/graphene tunnel devices offer promise as sensitive mid-infrared photodetectors but the microscopic origin underlying the photoresponse in them remains elusive. In this work, we investigated the photocurrent generation in graphene/hBN/graphene tunnel structures with localized defect states under mid-IR illumination. We demonstrate that the photocurrent in these devices is proportional to the second derivative of the tunnel current with respect to the bias voltage, peaking during tunneling through the hBN impurity level. We revealed that the origin of the photocurrent generation lies in the change of the tunneling probability upon radiation-induced electron heating in graphene layers, in agreement with the theoretical model that we developed. Finally, we show that at a finite bias voltage, the photocurrent is proportional to either of the graphene layers heating under the illumination, while at zero bias, it is proportional to the heating difference. Thus, the photocurrent in such devices can be used for accurate measurements of the electronic temperature, providing a convenient alternative to Johnson noise thermometry.

New Generation of Superattenuator for Einstein Telescope: preliminary studies

Seismic noise and local disturbances are dominant noise sources for ground-based gravitational waves detectors in the low frequency region (0.1–10 Hz) limiting their sensitivity and duty cycle. With the introduction of high-performance seismic isolation systems based on mechanical pendula, the 2nd generation laser interferometric detectors have reached the scientific goal of the first direct observation of GW signals thanks to the extension of the detection bandwidth down to 10 Hz. Now, the 3rd generation instrument era is approaching, and the Einstein telescope giant interferometer is becoming a reality with the possibility to install the detector in an underground site where seismic noise is 100 times smaller than on surface. Moreover, new available technologies as well as the experience acquired in operating advanced detectors are key points to further extend the detection bandwidth down to 2 Hz with the possibility to suspend cryogenic payload and then mitigating thermal noise too. Here, we present a preliminary study devoted to improving seismic attenuation performance of the advanced VIRGO superattenuator in the low frequency region of about five orders of magnitude. Particular care has been carried on in analyzing the possibility to improve the vertical attenuation performance with a multi-stage pendulum chain equipped with magnetic anti-springs that is hung to a double inverted pendulum in nested configuration. The feedback control requirements and possible strategies to be adopted for this last element will be presented.

Feasibility of acousto-electric tomography

Abstract In acousto-electric tomography (AET) the goal is to reconstruct the electric conductivity in a domain from electrostatic boundary measurements of corresponding currents and voltages, while the domain is perturbed by a time-dependent acoustic wave, thus taking advantage of the acousto-electric effect. We approach the AET reconstruction in two steps: First, the interior power density is obtained from boundary measurements by solving a linear inverse and ill-posed problem; second, the interior conductivity is reconstructed from the power density by solving a non-linear and well-posed problem. Mathematically these inverse problems are fairly well understood, and reconstruction methods work well on synthetic data. This is in contrast to experimental findings. An effect can indeed be observed and data can be collected. However, the acousto-electric coupling is very weak, and consequently, the change in the measured voltage due to the acoustic perturbation might be too small compared to the background noise for viable reconstructions. 

In this paper, we take one step towards understanding the feasibility of AET. We provide an in-silico model of the coupled physics scenario based on standard models for the individual phenomena. Moreover, we formulate and implement numerically a full reconstruction method for the inverse problem via the two steps. We perform computational experiments with realistically chosen parameters from the context of medical imaging. The focus is on understanding the role of the acousto-electric coupling parameter and the signal-to-noise ratio (SNR). The critical signal strength is analyzed and the omnipresent Johnson-Nyquist noise is estimated. We obtain both positive and negative findings; we can reconstruct features even under severe noise conditions, but we also find that the SNR one is likely to face in practice is too low to obtain useful reconstructions.

Role of spontaneous thermal emissions in inflationary laser Raman instability

The role of thermal fluctuations on the stimulated Raman backscattering instability is investigated by means of Vlasov and particle-in-cell (PIC) simulations in a regime of strong linear Landau damping of the Langmuir wave. The instability is initially convective and amplifies thermal noise, leading to a low-amplitude back-scattered laser sideband. Linear Landau damping of the Langmuir sideband modifies and flattens the electron velocity distribution function at the resonant velocity, leading to a gradual decrease in the Landau damping rate and an increase in the convective amplification. The Langmuir wave traps electrons resulting in a rapid nonlinear absolute instability and large amplitude flashes of backscattered light off large amplitude Langmuir waves with trapped electrons, leading to the production of hot electrons. Conditions for simulating realistic thermal noise with Vlasov and PIC simulations are discussed and defined.

Stacking and ridge regression-based spectral ensemble preprocessing method and its application in near-infrared spectral analysis

Spectral preprocessing techniques can, to a certain extent, eliminate irrelevant information, such as current noise and stray light from spectral data, thereby enhancing the performance of prediction models. However, current preprocessing techniques mostly attempt to find the best single preprocessing method or their combination, overlooking the complementary information among different preprocessing methods. These preprocessing techniques fail to maximize the utilization of useful information in spectral data and restrict the performance of prediction models. This study proposed a spectral ensemble preprocessing method based on the rapidly developing ensemble learning methods in recent years and the ridge regression (RR) model, named stacking preprocessing ridge regression (SPRR), to address the aforementioned issues. Different from conventional ensemble learning methods, the proposed SPRR method applied multiple different preprocessing techniques to the original spectral data, generating multiple preprocessed datasets. These datasets were then individually inputted into RR base models for training. Ultimately, RR still served as the meta-model, integrating the output results of each RR base model through stacking. This approach not only produced diversity in base models but also achieved higher accuracy and lower computational complexity by using a single type of base model. On the apple spectral dataset collected by our team, correlation analysis showed significant complementary information among the data produced by different preprocessing techniques. This provided robust theoretical support for the proposed SPRR method. By introducing the currently popular averaging ensemble preprocessing method in a comparative experiment, the results of applying the proposed SPRR method to six datasets (apple, meat, wheat, olive oil, tablet, and corn) demonstrated that compared to the single preprocessing method and averaging ensemble preprocessing method, SPRR yielded the best accuracy and reliability for all six datasets. Furthermore, under the same conditions of the training and test datasets, the proposed SPRR method demonstrated better performance than the four commonly used ensemble preprocessing methods.

Microseismic Observation Enabled by High-Sensitivity Micromechanical Interferometers

High-sensitivity accelerometry has historically been employed to explore Earth sciences and advance resource-related industries, such as petroleum exploitation. The devices capable of such measurements, however, traditionally involve precise mechanical structures and consequent large dimensions. In this work, combined by micromechanical systems and grating-assisted interferometry, a closed-loop optical accelerometer with nano-g (ng) sensitivity is developed for microseismic observations. In order to lower the intrinsic thermal noise, a modified 8.84 Hz micromechanical spring-mass oscillator is designed and fabricated. Additionally, an active control system is equipped to stabilize the device temperature and thus enhance the low-frequency stability. Field tests demonstrate that the prototype has achieved a scale factor of 1195 V/g, along with a dynamic range of 1.12 mg and a bandwidth of about 7 Hz. Further, under the controlled 45 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 0.01 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> C temperature condition, complete terrestrial microsesimic peaks from 0.1 Hz to 3 Hz are tracked. After calibration by a reference seismometer, the device self-noise is determined as 2 ng/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sqrt{Hz}$</tex-math></inline-formula> from 0.2 Hz to 4 Hz with a bias stability of 7.9 ng. The transducer and control circuits are both packaged within a 13.6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\times 13.6\times$</tex-math></inline-formula> 12.8 cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> insulated enclosure, making it advantageous for outdoor observations.

First upper limits on the 21 cm signal power spectrum from cosmic dawn from one night of observations with NenuFAR

The redshifted 21 cm signal from neutral hydrogen is a direct probe of the physics of the early universe and has been an important science driver of many present and upcoming radio interferometers. In this study we use a single night of observations with the New Extension in Nan cay Upgrading LOFAR (NenuFAR) to place upper limits on the 21 cm power spectrum from cosmic dawn at a redshift of $z$ = 20.3. NenuFAR is a new low-frequency radio interferometer, operating in the 10--85 MHz frequency range, currently under construction at the Nan cay Radio Observatory in France. It is a phased array instrument with a very dense $u coverage at short baselines, making it one of the most sensitive instruments for 21 cm cosmology analyses at these frequencies. Our analysis adopts the foreground subtraction approach, in which sky sources are modeled and subtracted through calibration and residual foregrounds are subsequently removed using Gaussian process regression. The final power spectra are constructed from the gridded residual data cubes in the $u plane. Signal injection tests are performed at each step of the analysis pipeline, the relevant pipeline settings are optimized to ensure minimal signal loss, and any signal suppression is accounted for through a bias correction on our final upper limits. We obtain a best 2sigma upper limit of $2.4 mK $ at $z$ = 20.3 and $k$ = 0.041 $h\ cMpc $. We see a strong excess power in the data, making our upper limits two orders of magnitude higher than the thermal noise limit. We investigate the origin and nature of this excess power and discuss further improvements to the analysis pipeline that can potentially mitigate it and consequently allow us to reach thermal noise sensitivity when multiple nights of observations are processed in the future.

High stability of dark current enables stretchable near-infrared self-powered organic photodetectors

Ultra-flexible and stretchable organic photodetectors (s-OPDs) sensitive in the near-infrared (NIR) region hold great potential for wearable health monitoring with excellent physiological signal and skin conformability. However, the development of OPDs that combines NIR sensitivity, low power consumption, low cost, simple fabrication structure, and good mechanical properties is still challenging and has not been well explored. In this work, we report a self-powered s-OPD with a simple fabrication structure used for organic solar cells and a detectivity of more than 1 × 1012 Jones (corrected by noise current) in the NIR region at 10% tensile strain and short response time (2.46 μs), representing state-of-the-art performances. Reducing energetic disorders other than discrete traps in photoactive layers is more crucial to further reduce the dark current at zero bias. The dark current of the OPDs exhibits higher mechanical stability than photocurrent due to the slower degradation of the parallel resistance than the series resistance under tensile strain. The higher stability of dark current enables the s-OPDs as a stretchable organic photoplethysmogram heart rate sensor, showing excellent detectivity under 30% strain or 800 stretching–release cycles at 10% strain, indicating the great potential for application in wearable optoelectronics.

Quantum Parallel Training of a Boltzmann Machine on an Adiabatic Quantum Computer

AbstractDespite the anticipated speed‐up of quantum computing, the achievement of a measurable advantage remains subject to ongoing debate. Adiabatic Quantum Computers (AQCs) are quantum devices designed to solve quadratic uncostrained binary optimization (QUBO) problems, but their intrinsic thermal noise can be leveraged to train computationally demanding machine learning algorithms such as the Boltzmann Machine (BM). Despite an asymptotic advantage is expected only for large networks, a limited quantum speed up can be already achieved on a small BM is shown, by exploiting parallel adiabatic computation. This approach exhibits a 8.6‐fold improvement in wall time on the Bars and Stripes dataset when compared to a parallelized classical Gibbs sampling method, which has never been outperformed before by quantum approaches.

Convolutional denoising for large-volume Seebeck calorimeter

Ambient temperature fluctuations can affect the thermal noise and sensitivity of a large-volume Seebeck calorimeter. This paper proposes that a reference cell considerably smaller than the sample cell in the apparatus can effectively neutralize this noise. It is found that the thermal signals from both the reference and sample cells exhibit a convolution relationship. By deconvolving two distinct thermal pulses generated by abrupt changes in cooling fluid temperature, one from the reference cell and one from the sample cell, a corresponding response function is derived. And using this function, the noise is canceled out by subtracting the convoluted signal of the reference cell from that of the sample cell during isothermal calorimetry. Experimentally, utilizing this technique with two calorimeters, one with a 17.6-liter capacity and the other with a 27-liter capacity, has been shown to reduce noise by at least 5 % and 6 % from their initial values, respectively.

Offline Fault Diagnosis for 2-Level Inverter: Short-Circuit and Open-Circuit Detection

Fault detection is very important to improve the reliability of power conversion devices. Faults of power semiconductors can be broadly divided into shorts and opens and are further classified into two types depending on whether there is an internal problem with the switch or anti-parallel diode. In this paper, fault-diagnosis methods for short-circuit and open-circuit states are proposed, respectively. A method of classifying and diagnosing faults by applying a gate signal to each switch is proposed to diagnose short-circuit conditions. This method uses only current magnitude information, which reduces the amount of required information and reduces diagnostic failures due to angle errors and current noise. A method is proposed to detect a faulty switch by applying a voltage vector and comparing the current angle with a lookup table to diagnose an open state. An iterative diagnostic algorithm is proposed to prevent diagnostic failure due to angle error and current noise. The effectiveness of the proposed diagnosis method is verified through experiments and simulations.

Transportation Noise Pollution and Cardiovascular Health.

Epidemiological studies have found that transportation noise increases the risk for cardiovascular morbidity and mortality, with solid evidence for ischemic heart disease, heart failure, and stroke. According to the World Health Organization, at least 1.6 million healthy life years are lost annually from traffic-related noise in Western Europe. Traffic noise at night causes fragmentation and shortening of sleep, elevation of stress hormone levels, and increased oxidative stress in the vasculature and the brain. These factors can promote vascular (endothelial) dysfunction, inflammation, and arterial hypertension, thus elevating cardiovascular risk. The present review focusses on the indirect, nonauditory cardiovascular health effects of noise. We provide an updated overview of epidemiological research on the effects of transportation noise on cardiovascular risk factors and disease, and mechanistic insights based on the latest clinical and experimental studies and propose new risk markers to address noise-induced cardiovascular effects in the general population. We will discuss the potential effects of noise on vascular dysfunction, oxidative stress, and inflammation in humans and animals. We will elaborately explain the underlying pathomechanisms by alterations of gene networks, epigenetic pathways, circadian rhythm, signal transduction along the neuronal-cardiovascular axis, and metabolism. We will describe current and future noise mitigation strategies. Finally, we will conduct an overall evaluation of the status of the current evidence of noise as a significant cardiovascular risk factor.

Impact of interface traps and noise analysis on dual material graded channel CGAA FET: A device reliability

This paper explores the effects of changing the device's parameters, such as the gate length (Lg), nanowire radius (r), oxide thickness (tox), and frequency (f), on the noise characteristics of dual material graded channel (DMGC) cylindrical gate all around (CGAA) FET while considering the presence and absence of interface trap charges. The performance analysis of the DMGC CGAA FET with that of the SMGC (single material graded channel) CGAA FET, is carried out while taking into account the impact of trap charges. It's noteworthy that the DMGC FET demonstrates significant advantages, with improvement in Ion/Ioff, reduction in DIBL, and SS when compared to the SMGC CGAA FET, both in the cases of without and with traps. The investigation also extends to analyse the analog/RF performance of the DMGC FET, for different type of trap charges. Furthermore, the power spectral densities of current noise (Sid) and voltage noise (Svg) are examined by varying the device dimensions and temperature. This also addresses the various sources of noise, including flicker noise (1/f), generation-recombination (G-R) noise, and diffusion noise. These types of noise have different prevalence depending on the operating frequency. At low frequencies, flicker and G-R noises dominate, while at higher frequencies, diffusion noise becomes the prominent factor impacting the device's performance. The research findings indicate that the optimal performance of the DMGC CGAA FET is achieved with smaller nanowire radius and thinner oxide thickness, regardless of trap charges. These findings offer valuable insights for improving the design and performance of DMGC CGAA FET in low power applications.

Eliminating sensing blind spots of field-enhanced Rydberg atomic antenna via an asymmetric parallel-plate resonator

Due to its large electric dipole moment, the Rydberg atom exhibits a strong response to weak electric fields, hence it is regarded as a highly promising atomic antenna. However, to enhance the reception sensitivity, split-ring resonators are needed normally, which will brings sensing blind spots. Thus it is not conducive to the application of full-coverage space communication. Here we propose that an atomic antenna with an asymmetric parallel-plate resonator, can not only enhance the received signal, but also eliminate sensing blind spots (pattern roundness can reach 7.8 dB while the split-ring resonator can be up to 39 dB). We analyze the influence of structural parameters on the field enhancement factor and directionality, and further discuss the limitation of the sensitivity by using thermal resistor noise theory. This work is expected to pave the way for the development of field-enhanced Rydberg atomic antennas that communicate without a blind spot.

Dynamics of atom-atom entanglement in two-atom model with degenerate two-photon raman transitions

The exact dynamics of a model consisting of two two-level atoms interacting with the electromagnetic field mode of an ideal resonator through degenerate Raman transitions are found for coherent and thermal field states. The exact solution is used to calculate atom-atom negativity. It is shown that for separable initial states of atoms, their interaction with the resonator field does not lead to the occurrence of atom-atom entanglement. It was found that for the Bell initial states of atoms in the case of a coherent resonator field, the effect of sudden death of entanglement takes place for large average values of the number of photons in the resonator, while in case of thermal noise, this effect is absent for any intensities of the resonator field.